Caerphilly Castle is the largest castle in Wales and the second largest in Britain after Windsor castle. It is also one of the largest fortresses in Europe and is cunningly surrounded by shallow lakes to slow attackers and prevent tunnelling. Unlike most of the other castles in Wales Caerphilly was not build by Edward I during his crack down on Welsh resistance. It was instead built in 1271 by Gilbert ‘the Red’ de Clare, a powerful nobleman of Norman descent who was squabbling with another nobleman of Welsh origin, Llywelyn. Thanks: Tom